DESCRIPTION

The devfs_xxx_cdevpriv() family of functions allows the cdev driver
methods to associate some driver-specific data with each user process
open(2) of the device special file. Currently, functioning of these
functions is restricted to the context of the cdevsw switch method calls
performed as devfs(5) operations in response to system calls that use
filedescriptors.
The devfs_set_cdevpriv() function associates a data pointed by priv with
current calling context (filedescriptor). The data may be retrieved
later, possibly from another call performed on this filedescriptor, by
the devfs_get_cdevpriv() function. The devfs_clear_cdevpriv()
disassociates previously attached data from context. Immediately after
devfs_clear_cdevpriv() finished operating, the dtr callback is called,
with private data supplied data argument.
On the last filedescriptor close, system automatically arranges
devfs_clear_cdevpriv() call.
If successful, the functions return 0.
The function devfs_set_cdevpriv() returns the following values on error:
[ENOENT] The current call is not associated with some
filedescriptor.
[EBUSY] The private driver data is already associated with
current filedescriptor.
The function devfs_get_cdevpriv() returns the following values on error:
[EBADF] The current call is not associated with some
filedescriptor.
[ENOENT] The private driver data was not associated with
current filedescriptor, or devfs_clear_cdevpriv() was
called.